Burette apparatus

ABSTRACT

There is provided a burette apparatus having a delivery tube connecting a fluid bag to a burette assembly, via a fluid entry spigot formed in an end cap assembly of the burette assembly, the end cap assembly having a bypass spigot connected to the delivery tube and usually closed by clip, to allow an override for adding liquid to the burette. The end cap assembly closes the upper end of the transparent, cylindrical burette body, into which extends a stainless steel tube extension of the fluid entry spigot, the lower end of the burette body being closed by a lower closure assembly having a check valve and a drip chamber. An outlet tube passes from the drip chamber to the patient via regulating clamp. A float assembly is located in the burette body including an extension rod provided with a resilient cup adapted to engage the open end of the stainless steel tube extension.

This invention relates to burette apparatus.

This invention has particular but not exclusive application to buretteapparatus for administering intravenous (IV) liquids, and is describedhereinafter in relation to this application. However, this invention mayfind use in other applications, such as metering systems in industry orthe like.

Medical burettes are used to provide a reasonable precise flow rate fromIV supplies to patients and to provide a means of introducing secondaryfluids via a septum or the like. The precision of flow rate arises outof the isolation of the relatively short burette volume from the head ofthe IV source between fillings of the burette. Burettes uses toadminister IV fluids generally comprise a graduated cylinder adapted toreceive a selected volume of liquid from a collapsible container via amanually operable valve. The cylinder then delivers the IV fluid to adrip metering chamber providing a visual indication of flow rate, andthence to a selectively occludable drip line to the patient.

A disadvantage of the conventional system is that medical staff arerequired to periodically replenish the burette volume, which cannot bemade so large as to introduce a substantial variation between flow ratesbetween full and empty condition of the burette. In any case, thetypical 100 ml burette must be of a diameter such that secondaryadditions may be measured in against the graduations of the burette. Inpractice this tends to introduce a head pressure difference between thefull and low conditions that has an undesirable effect on flow ratesbetween the two conditions.

The present invention aims to substantially alleviate at least one ofthe above disadvantages and to provide burette apparatus which will bereliable and efficient in use. Other objects and advantages of thisinvention will hereinafter become apparent.

With the foregoing and other objects in view, this invention in oneaspect resides broadly in a burette apparatus including:

a burette body member having an inlet connected to a source of liquidand an outlet;

control means adapted to maintain the liquid level in said body memberwithin a range;

metering means for controlling the rate of flow of said liquid throughsaid outlet, and

closure means for said outlet operable at a minimum liquid level in saidbody member.

The burette body member may take any suitable form. For example, thebody member may comprise a substantially transparent body member havingits inlet in the region of the top and its outlet in the region of thebottom such that the fluid may be delivered by gravity. The body membermay comprise a cylindrical portion adapted to be supported substantiallyvertically and upper and lower end closure portions including the inletand outlet respectively.

The body member may be graduated such that the immediate liquid leveltherein may be determined. The body member may be provided withancillary features such as secondary fluid injection points.

The inlet to the body member may include any suitable inlet assemblyproviding fluid connection to the liquid source. In the case of singleuse IV drip bags, the conventional delivery means for such fluids, theinlet assembly may include a flexible tube adapted to connect theburette inlet with the outlet of the bag, which is generally suspendedin use above the burette. The inlet assembly may include vapour lockavoidance means, flow control valves and/or other conventional featuresof such assemblies.

The control means adapted to maintain the liquid level in said bodymember within a range may take the form of a condition responsive flowcontrol assembly comprising a selectively operable closure means andoperating means therefor, the operating means being responsive to theliquid level in the burette. For example, the control means may comprisean electronic level monitoring means and electromechanical valve meansfor selectively admitting said liquid.

Alternatively, the control means may comprise a float operated valve.For example, the control means may comprise a float located in said bodymember and adapted to operate a linear valve adapted to close the inletupon a maximum fluid level being reached and to maintain the fluid levelbetween that maximum and a minimum level. The linear valve may forexample comprise a rubber or other resilient seat adapted to sealinglyclose an aperture providing fluid communication between the inlet andthe interior of the body member. The seat may alternatively comprise acup-like portion adapted to engage the aperture to provide sealingagainst the surface tension of a small quantity of liquid present in thecup. Preferably, the seat comprises a combination cup-shaped resilientseat to provide precise closure against the surface tension and positiveclosure against the resilient material.

The aperture advantageously comprises the end of a metal or other tubeassembled to the end portion of the preferred cylindrical body memberand forming part of the inlet assembly.

Preferably, the float, seat and tube end are mounted substantiallycoaxial with the preferred cylindrical burette body portion. The floatmay be provided with guide portions adapted to maintain the float insubstantial concentricity with the preferred cylindrical body portion,whilst permitting the relatively free passage of fluid between the inletand the body member when the control means so permits.

Preferably, the addition of secondary liquids to the body member causesthe control means to close off flow until the level drops to the bottomof the range. The liquid level range controlled by the control means ispreferably a minimum amount. For example, in apparatus adapted toreplace a conventional 100 ml burette, the range may be 2 ml or evenless, between for example 8 to 10 ml in the body member. By this means,variation in head pressure in the burette is substantially eliminatedand the frequency of carer visits required is reduced simultaneously.

In order to provide for adequate secondary liquid volumes whilstoperating over a narrow liquid level range for the primary liquid toreduce head variation, the body member preferably has a capacity inexcess of said liquid level range to accommodate the secondary liquidaddition. The float means may support the resilient seat atop a supportmember adapted to span the expected secondary liquid space, preferablyextending coaxially with the cylindrical body portion. If desired thesupport means may take the form of a rod or the like and may alsofunction as an upper guide for the float and rod assembly, whencooperating with complementary guide means associated with the bodymember.

The outlet for said body member may comprise an aperture allowing liquidto pass into a delivery tube or the like connected to a patient.Preferably, the outlet comprises an outlet assembly formed in an endclosure portion of the body member.

The metering means for controlling the rate of flow of the liquidthrough the outlet may comprise a variable valve or limiting aperture orthe like. Preferably, the metering means includes flow meter meanswhereby an indication of the flow rate may be given. For example, themetering means may comprise a variable clamp type valve disposed in adelivery line connected to the outlet, and used in conjunction with avisual drip indicator forming an outlet assembly with the end closureportion of the body member.

The closure means for said outlet may be operable to close off the flowby any suitable means responsive to the liquid level dropping below apredetermined minimum liquid level in the body member, such as when theliquid supply expires or is interrupted. The closure means may comprisea captive floating ball adapted to sealably engage a seat disposedacross the outlet, the ball housing and seat advantageously beingintegrally formed in the outlet assembly comprising an end portion ofthe housing member.

Alternatively, in float operated apparatus, the closure means maycomprise a sealing portion of the float adapted to sealingly engage theoutlet when the float drops below a predetermined level. For example,the outlet may include a hollow tubular portion, preferably an extensionof the preferred drip metering tube, extending up into the housing andadapted to sealably engage a resilient seat provided in the underside ofthe float.

Of course, the sealing arrangement may comprise a needle associated withthe float and adapted to seal against a seat disposed about the outlet.

The burette body member head space may be vented or unvented. If theburette body member headspace is vented, it is preferably isolated fromthe atmosphere by communication with the preferably sterile headspace ofthe liquid supply container. In one embodiment, there is providedcomplementary connector means for joining the burette body member and aliquid supply reservoir. The connector portion associated with theburette body portion is provided with penetrating conduits adapted topenetrate single-use sealing members provided over aperture associatedwith the connector portion of the liquid supply container. Typically twosuch complementary pairs are provided in a one-way assembly connectorone pair connecting the respective head spaces of the burette body andthe liquid container and the other pair allowing communication of thefluid with the control means.

Apparatus as described above generally avoids flow variation by reducingthe head variation in the burette to a minimum, without increasing nursevisits for refilling. However, in a further aspect, this inventionincludes embodiments where the metering means is adapted to provide aflow rate which is substantially independent of the actual physical headin the burette.

For example the metering means may comprise a float assembly including avariable aperture metering assembly configured such that at high headsthe aperture allows substantially the same flow as at low heads. Such anarrangement may include, for example, a tapered needle adapted to passinto a metering tube and selected as to taper, length and relativedimensions to provide the requisite flow characteristic across the headrange of a conventional burette or even a burette of greatly increasedcapacity.

In order that this invention may be more readily understood and put intopractical effect, reference will now be made to the accompanyingdrawings which illustrate a preferred embodiment of the invention andwherein:

FIG. 1 is a partially cut away side view of apparatus in accordance withthe present invention.

In the figure there is illustrated burette apparatus adapted for usewith a conventional sterile liquid supply bag 10, having a deliveryspigot 11 and a septum-covered injection spigot 12, and adapted to besuspended on an infusion stand by means of integrally formed suspensiontag 13. A delivery tube 14 connects the delivery spigot 11 to a buretteassembly 15, via a fluid entry spigot 16 formed in an end cap assembly17 of the burette assembly 15. The delivery tube 14 is closable by avalve clamp 20.

The end cap assembly 17 is provided with a bypass spigot 21 adapted tobe connected back to the delivery tube 14 at Y-piece 22, usually pressedclosed by closure clip 23, to allow an override for adding liquid to theburette when the fluid entry spigot 16 is occluded as hereinafterdescribed. The end cap assembly 17 is also provided with a utilityspigot 24, in this example providing a sterile vent 25 thoughmicroporous cap 26, and an injection point 27 for secondary fluidthrough septum 30.

The end cap assembly 17 closes the upper end of a transparent,cylindrical burette body 31, into which extends a stainless steel tubeextension 32 of the fluid entry spigot 16.

The lower end of the burette body 31 is closed by a lower closureassembly 33 comprising an integral ball housing and seat 34 containing afloating check ball 35, and being in fluid communication with atransparent drip chamber 36 via a stainless steel tube 37. An outlettube 40 passes from the drip chamber 36 to the patient via regulatingclamp 41.

A float assembly 42 is located in the burette body 31 and comprises afloat body 43 having locating lugs 44 disposed about its periphery, andan extension rod 45 extending upwards, the extension rod 45 beingconstrained to the axis of the burette body 31 by guide plate 46. Theguide plate 46 has passages 47 to permit free fluid passage thereby. Theupper end of the extension rod 45 is provided with a resilient cup 50adapted to engage the open end of the stainless steel tube extension 32.

In use, the bag 10 is fitted to the burette assembly 15 and the flow iscommenced to purge the system. The cannula assembly (not shown) ispurged in the usual manner and fitted to the patient. The regulatingclamp is adjusted to the desired drip rate, as is the case with aconventional burette. As the fluid level drops in the burette assembly15, the float body 43 also drops, pulling the cup 50 off the stainlesssteel tube extension 32. When the stainless steel tube extension 32clears the maniscus of any fluid in the cup, the liquid can flow intothe burette assembly 15 until the stainless steel tube extension 32seals against the cup 50 again. In the present embodiment the range ofvolume in the apparatus is 2.5 ml to 11 ml, which, over the diameter ofthe burette body, represents very much less of a head variation thanthat imposed by the remaining components downstream such as the dripchamber 36. When the bag 10 empties, the float drops to the bottom ofthe burette assembly 15 and, as the liquid level passes down into theball housing and seat 34, the floating check ball 35 seals the outlet toprevent air passing therethrough.

Apparatus in accordance with the foregoing embodiment has severalparticular advantages. By virtue of its operation as a closed systemrequiring a minimum of intervention, the apparatus is usable under awide range of conditions generally considered as adverse for IVadministration, such as underwater to SCUBA divers or in low gravityconditions. Since the apparatus is self regulating, the addition ofsecondary fluids via the side port septum does not affect the careregime insofar as nurse visits is concerned, since the apparatus willrecommence primary fluid flow when the level of secondary fluid allowsthe float to pull the primary valve open. The apparatus is amenable tovented or unvented use.

It will of course be realised that while the above has been given by wayof illustrative example of this invention, all such and othermodifications and variations thereto as would be apparent to personsskilled in the art are deemed to fall within the broad scope and ambitof this invention as defined in the claims appended hereto.

We claim:
 1. A burette apparatus comprising:a burette body member havingan inlet connected to a source of liquid and an outlet for allowingliquid to pass through the body; control means for maintaining a liquidlevel in said body member, said control means comprising an inlet stubprojecting into the body member from the inlet for directing the sourceof a liquid into the body, and a displaceable float assembly having acup portion and a sealing fluid therein for stopping a liquid flow fromthe inlet stub when said inlet stub contacts the liquid of the cup;metering means for controlling a rate flow of said liquid through saidoutlet; and outlet closure means operable at a minimum level of saidliquid in said body member.
 2. Burette apparatus according to claim 1,wherein said burette body member comprises a cylindrical portionsupported substantially vertically, and upper and lower end closureportions including said inlet and outlet respectively.
 3. Buretteapparatus according to claim 2, wherein said upper end closure portionis provided with a secondary fluid injection point.
 4. Burette apparatusaccording to claim 1, wherein said inlet to the body member comprises aninlet assembly providing fluid connection to a bag type liquid sourcevia a flexible tube connecting the inlet with an outlet of the bag. 5.Burette apparatus according to claim 1, wherein said body member has acapacity in excess of said liquid level to accommodate secondary liquidaddition.
 6. Burette apparatus according to claim 5, wherein said cupportion comprises a rubber or other resilient seat closing said inletwhen urged thereagainst by liquid in excess of said maximum level. 7.Burette apparatus according to claim 1, wherein said outlet comprisespart of an outlet assembly formed in an end closure portion of the bodymember.
 8. Burette apparatus according to claim 7, wherein said meteringmeans comprises a variable valve or aperture.
 9. Burette apparatusaccording to claim 7, wherein said outlet closure means is operable inresponse to the liquid level dropping below a predetermined minimumliquid level in the body member.
 10. Burette apparatus according toclaim 9, wherein said outlet closure means comprises a captive floatingball sealably engaging a seat disposed across the outlet.
 11. Buretteapparatus according to claim 9, wherein said outlet closure meanscomprises a sealing portion of said float sealingly engaging the outletwhen the float drops below a predetermined level.
 12. Burette apparatusaccording to claim 8, wherein said metering means for controlling therate of flow of the liquid through the outlet comprises a variable clampdisposed on said delivery tube.
 13. Burette apparatus according to claim12, wherein said metering means includes flow meter means whereby anindication of the flow rate may be given.
 14. Burette apparatusaccording to claim 13, wherein said flow meter means comprises a visualdrip indicator forming part of said outlet assembly.
 15. Buretteapparatus according to claim 1, wherein a headspace in said body memberis vented to the atmosphere.
 16. Burette apparatus according to claim 1,wherein a headspace in said body member is vented to a correspondingheadspace in said source of liquid.
 17. Burette apparatus according toclaim 16, wherein the connection between said liquid source and saidinlet is made by means of complementary connector means including meansproviding for said headspace in said body member to vent to saidcorresponding headspace in said source of liquid.
 18. Burette apparatusaccording to claim 1, wherein the connection between said liquid sourceand said inlet is made by means of complementary connector meansincluding selectively operable bypass means enabling manually selectivefluid flow into said body member.